Two new quinolone aniibacterials, difloxacin (A-56619) and sarafloxacin (A-56620), were compared with oxolinic acid, oxytetracycline, and ormetoprim-sulfadimethoxine in vitro for their activities against common bacterial pathogens offish. The objectives were to determine (1) the frequencies of in vitro resistance to antibacterials at eight times the minimum inhibitory concentration (MIC), (2) the rates and extents of decrease in antibacterial susceptibility when organisms were serially transferred to increasing concentrations of drug, (3) the stability of the decreased susceptibility, and (4) cross-resistance to other antibacterials by organisms with developed resistance. The frequency of spontaneous resistance to all antibacterials at eight times the MIC was low, 10~7-10" 10 . Quinolone-selected mutants that showed low-level resistance would be inhibited by achievable in vivo levels of difloxacin or sarafloxacin. Oxolinic acid would not inhibit such mutants. The rate of susceptibility decrease during serial transfer was gradual and stepwise for all organism-drug combinations. In contrast to difloxacin and sarafloxacin, MICs of oxolinic acid, oxytetracycline, and ormetoprim-sulfadimethoxine for some final transfer cultures were above achievable serum levels. Developed resistance was stable for all antibacterials. Cross-resistance was seen among the three quinolones but was not seen with the other antibacterials, except for oxytetracycline. Based on results, resistance to difloxacin and sarafloxacin by fish pathogens will not develop easily during proper therapeutic use.

The in vitro antibacterial potencies of A-56619 and A-56620, two new aryl-fluoroquinolones, were compared with the potency of norfloxacin against a broad spectrum of organisms. Cefotaxime, aztreonam, piperacillin, imipenem, penicillin, and gentamicin were also tested for reference purposes. The MICs required to inhibit at least 90% of the strains tested ranged from 0.25 to 4 p,g/ml for A-56619 and from 0.06 to 0.5 ,ug/ml for A-56620 for members of the Enterobacteraceae. A-56619 was generally twofold less potent and A-56620 was twofold more potent than norfloxacin against most aerobic gram-negative bacilli, including members of the Enterobacteriaceae and Pseudomonas aeruginosa. Against indole-positive Proteus, MorganeUa, Providencia rettgeri, and Serratia strains, A-56619 was at least 8-to 16-fold less potent than norfloxacin. A-56619 and A-56620 were four-to eightfold more potent than norfloxacin against Staphylococcus aureus and equally potent to fourfold more potent against Streptococcus species, Haemophilus influenzae, and Neisseria gonorrhoeae. The MICs of A-56619 aq4 A-56620 were only slightly affected by increased inoculum size or by the addition of various cations at physiologic concentrations. A-56619 was three-to fivefold less active at pH 8.0 than at pH 6.5 or 7.2. A-56620 was twofold less active at pH 6.5 than at pH 8.0 or 7.2 against members of the Enterobacteriaceae and Pseydmonas aeruginosa; similar pH variations did not affect A-56620 activity against gram-positive cocci. The potencies of A-56619, A-56620, and norfloxacin were less in urine than in Mueller-Hinton broth; however, this effect was more pronounced with norfloxacin. Human serum at a concentration of 50% caused a 4-to 64-fold decrease in the potency of A-56619 and an average 4-fold decrease in the potency of A-56620, compared with no efect on the potency of norfioxacin. A-56619, A-56620, and norfloxacin were bactericidal and, at four times the MIC, reduced the viable cell counts of Escherichia coli, Staphyloeoccus aureus, and Pseudomonas aeruginosa by approximately 99.9% within 2 h. A-56619, A-56620, and norfloxacin showed no significant synergistic activity and no gntagonism when they were combined with aminoglycoside or j-lactam antimicrobial agents.

The aerobic biodegradation of sarafloxacin hydrochloride, a fluoroquinolone antibiotic registered for use against poultry diseases, was tested in three soils: loam, silt loam, and sandy loam. Sarafloxacin treatment demonstrated mineralization to 14CO2 amounting to 0.58%, 0.49%, and 0.57% in loam, silt loam, and sandy loam soils, respectively, at the termination of the test. The extractability of sarafloxacin from soil in acetonitrile and water (ACN:H2O, 1:1, v/v) was less than 1% of the applied radioactivity. This was followed by extraction with pipemidic acid (a quinolone with structural similarity to sarafloxacin) and KOH (PIP:KOH), which resulted in ∼25% extractability in loam, ∼73% in silt loam, and ∼80% in sandy loam soils, with extractability increasing with decreasing organic matter content (5.8%, 2.5%, and 1.3%, respectively, for the three soils). The high‐performance liquid chromatography (HPLC) analysis of ACN:H2O extractable radioactivity showed several components, all of which were less than 1% of the applied radioactivity. Hence, no attempt was made to characterize these components. The HPLC analysis of PIP:KOH extracts demonstrated two major components, one with a retention time of ∼4 to 5 min (designated polar component), the other component, sarafloxacin, with a retention time of ∼35 min. The components present in ACN:H2O or PIP:KOH extracts were not significantly different at day zero or at termination, prompting experiments that resulted in the following observations. Sarafloxacin standard exposed to extraction solvents (PIP:KOH and ACN:H2O) showed no degradation, suggesting stability of the test article in extraction solvents. Component profiles in sterile soils were similar to those in nonsterile soils, suggesting that the formation of the polar degradate component of sarafloxacin is an abiotic phenomenon. Experiments conducted with sand spiked with sarafloxacin showed very little or no transformation, suggesting that the degradation is a soil‐related phenomenon. The polar component was converted to sarafloxacin when the extracts were subjected to acid hydrolysis.

The in vitro antimicrobial activity of fortimicin A, the most active member of the fortimicin complex, was compared with that of amikacin, gentamicin, sagamicin and tobramycin against 352 strains of Enterobacteriaceae and other medically significant organisms. Against most of these organisms fortimicin and amikacin had comparable levels of antimicrobial activity, generally slightly less than that of gentamicin, sagamicin or tobramycin. Fortimicin had relatively weak activity against Pseudomonas aeruginosa strains. Fortimicin shows many of the characteristics of other aminoglycoside antibiotics: (i) improved activity at alkaline pH, (ii) rapid, bactericidal action, (iii) reduced activity with increasing inoculum levels, and (iv) synergistic activity with penicillin against enterococci. The activity of fortimicin was compared to that of gentamicin, tobramycin and amikacin against a group of 95 naturally occurring, antibioticresistant Gram-negative bacilli other than Pseudomonas. The organisms were isolated from clinical sources and selected primarily for gentamicin resistance by the sensitivity disc test. Fortimicin showed excellent activity against this group of organisms. At a concentration of 6.2 mcg/ml, fortimicin inhibited the most strains (92.6%) followed by amikacin (90.5%), gentamicin (23.2 %) and tobramycin (8.4 %).Fortimicin A, the most active member of the fortimicin complex described thus far, is a new potent, broad-spectrum antibiotic of the aminoglycoside type.1,2) This study was done in order to expand on the previous in vitro observations and to compare and contrast the properties of fortimicin A with clinically useful aminoglycosides. Materials and Methods MIC DeterminationThe minimum inhibitory concentration (MIC) of the antibiotics was determined by the agar dilution method,3) using the inocula replicating device of STEERS et al.4) Inoculum was adjusted so as to deposit approximately 101 CFU (colony forming units) per point of application. MUELLER-HINTON agar, pH 7.4, was used for most determinations. Whole or chocolatized sheep blood, 5 %, was added for tests of Streptococcus and Haemophilus respectively.GC Agar Base plus supplement B (Difco) was used for ,Veisseria. Haemophilus and Neisseria were incubated in 5% CO2. One or more of the following organisms was included in every evaluation of sensitivity as a procedure control: Escherichia coli ATCC 25922, Staphylococcus aurens ATCC 25923, Pseudomonas aeruginosa ATCC 27853. MBC DeterminationThe minimum bactericidal concentration (MBC) of the antibiotics was determined by the broth dilution method3) using MUELLER-HINTON Broth, pH 7.4, with an inoculum level of 105 CFU/ml. The MBC was the lowest concentration of antibiotic which resulted in a minimum 99.9% reduction in initial microbial count after 24 hours incubation. Antibiotics